Washington Area Butterfly Club
We began plant propagation (of many species, including white turtlehead) last fall, as a part of some of our programs. We collected white turtlehead seeds from our small wild population. We collected them when the small, round seed pods were turning brown, which according to the notes that I kept, was in very early November. We planted them almost as soon as we collected them, directly into 4" square pots. We used a soil-less potting mixture for planting.
According to New England Wild Flower Society (NEWFS), the seed might need light to germinate. So, we used two methods. First, we planted some directly on the potting mix, and covered them with a light layer of sifted river sand (we sifted it so that only the coarser sand would remain...we threw out the finer sand.) The idea of sand was that quartz sand transmits some light, but it also should protect the seed from drying out or getting washed around by rains. We collected our river sand, but if you wanted to have an easier method, a NEWFS staff member recommends using #1 washed filter sand, from swimming pool stores. Either way, the layer of sand should be thin--perhaps 1/8" or less.
Our second method was to sow the seeds, and cover with a VERY thin layer of potting mix (a dusting), and then a little sand as well. I labeled my pots with the idea of being able to compare which method worked better. However, as spring got busy with programs, some pots had multiple plants and we transplanted some plants from pot to pot, so my record-keeping became less precise. I would personally recommend the first method, or you could try both.
Many of our native wildflowers germinate better if they get a period of "stratification," which is essentially a period of moist cold. So, once we had seeds in pots, we watered the pots and put them in a "cold frame." This is a cold frame in name only. Unlike a standard cold frame, this is not meant to trap warmth. Instead, it is an insulated area, which gives the seeds some protection from the extremes of freezing and thawing. Our cold frame is a 4' x 8' box (those are the exterior measurements), constructed of 2" x l0" lumber put up on its side. The bottom of the box is about 6" below the level of the surrounding dirt, so that we get a little advantage from the insulating effect of the earth (like in a cellar).
Once truly cold weather arrived in November, we covered this up with a sheet of 4' x 8' insulation (from Home Depot), shiny side out, supported with crossbeams so that it did not collapse with snow accumulation. Basically, the insulation moderates the temperature, keeping the seeds more uniformly cold during the winter. It is important to remove the insulation early enough the next year, so that as the weather warms, plants don't germinate in the cold frame and die from lack of light. NEWFS recommended removing the insulation in mid-February, although as I recall we actually uncovered ours a little later than that. By the way, for a great description of these cold frames (and a picture), check out the wonderful book Growing and Propagating Wildflowers of the U.S. and Canada.
I hope that doesn't sound too complicated. We use our cold frame for both wet meadow plants (like turtlehead, lobelias, and swamp roses) and drier-soil plants (like Jack-in-the-pulpit, persimmons, and dogwoods). So, we simply water our plants. On the other hand, this fall I plan to build one or two additional cold frames for use ONLY with wet meadow plants, and with these, I plan to line the bottom of the cold frame (with a rubber liner). This would make maitenance of the plants easier, because during the growing season we could sit the pots in an extremely shallow layer of water. Our cold frame is big enough for about 180 plants in 2" pots. If you do not need so many, it would be easy to scale the size down.
In spring, the turtlehead germinated, but it germinated gradually and grew VERY slowly. Some of our species, like swamp milkweed, were growing huge and our turtlehead was still extremely tiny. Quite frankly, it was discouraging. But once warmer weather hit (about June) the turtlehead plants really took off, and when they did, they started growing great. My conclusion is that seedling turtleheads need warm weather before they start to put on large growth. Our plants are now mostly 10-16" tall, and some of them are "bushy" with numerous branches/stems.
It's worth noting that our propagated white turtlehead looks somewhat different than wild white turtlehead. It is more compact, with more leaves in a smaller area. I presume this is because the plants in our cold frame get such good light, watering, and fertilizing.
In our experience using this method, white turtlehead was really fairly simple to propagate, and in fact many of our plants were seeded by 4th-6th grade students. (I will mention that I tried to propagate pink turtlehead at home, for my gardens. Although I used the same method, I had more trouble with that species.) We plan to do more propagation this fall, both by seeding into pots like we did last fall, and by direct-seeding onto prepared ground.